Indoor air pollution is produced by many sources including furniture and building materials, industrial activity, cooking and human metabolism. If nothing is done this pollution is detrimental to health and the quality of life. The main method for improving indoor air quality is dilution: fresh air is brought in from the outside. This is expensive because in a cold climate the air must be heated and in a warm climate it must be cooled and dehumidified.
Presently there is not a device available for cleaning large volumes of indoor air cheaply and efficiently. Mechanical filtration involves limited conductance and a pressure drop, necessitating large fans involving large energy consumption. In addition the filter must be changed and can itself become a source of bacteria. Electrostatic filtration does not cause a large pressure drop, but only removes pre-existing particles; it does not act on gas-phase pollution. Ozonolysis is used to remove odours but the chemical products of ozonolysis are often more hazardous than the original compounds, in addition there are important components of indoor air pollution that do not react with ozone. UV light is used to sterilize air in hospitals but this method removes only a very few specific types of pollution from the airstream.
U.S. Pat. No. 6,589,486 (Spanton) discloses an air purifying apparatus and method suitable for use in a standard forced air building Heating, Ventilating and/or Air Conditioning system (HVAC) of a building. The air is treated with ultraviolet (UV) radiation and ozone. The UV is germicidal and kills microorganisms, including both bacteria and viruses. The ozone cleans air and removes odours from air. Ozone in combination with UV radiation destroys microorganisms which are not killed by the UV radiation. Spanton does not disclose how to remove toxic gaseous contaminants and particles such as smoke and dust from the air. Thus Spanton does not suggest to control the process in order to optimize aerosol formation inter alia by ensuring a sufficient time to aerosol growth and/or by addition of aerosol formation accelerators such as water and ammonia.
US Patent Application 2004/0120845 (Potember et al.) discloses a method and apparatus for neutralizing airborne pathogens in ventilated air, and in heating or air conditioning systems. The system has a flow-through reaction chamber that contains a UV light source that emits short intense flashes of broad-spectrum UV light, a source of water vapour or spray, and an ozone generator. After the treatment with UV and ozone the air passes through a porous matrix and a solid support coated with an ozone removal catalyst. The passage through such matrix requires a sufficient pressure requiring substantial fan energy consumption. Furthermore Potember at al. do not disclose how to remove pollution from the air steam using the aerosol particle growth mechanism.
U.S. Pat. No. 5,656,242 (Morrow et al.) discloses an air purifier having a perforated plate between UV lamps and a porous air filter. Biological material is trapped by the filter and killed by the low dose of UV radiation which passes through the perforations in the plate. Filtered air passing through the plate is subjected to a high dose of UV radiation which sterilizes remaining biological material in the air. An electrostatic filter at the outlet may trap viruses which have been positively charged either by the action of the UV lamps or by positively charging the plate in order to strip electrons from the viruses. The UV lamps may be mercury lamps which are allowed to emit at both their ozone forming wavelength as well as the ozone breakdown wavelength. In such instance, a light filter surrounds the lamps which pass light only at the ozone breakdown wavelength. Air subjected to the unfiltered light is consequently exposed to ozone, which is a known biocide. The filtered light is in a zone which is filled with water mist such that hydroxyl radicals result. Air passing through this zone is scrubbed by the hydroxyl radicals. Morrow et al do not disclose how to treat the air with ozone before treatment with UV radiation. Morrow does not disclose removal of pollution via formation of aerosols. They do not control the dosage of ozone.
Electrostatic air purifiers are used to remove particles produced by welding. They are also marketed to clean indoor air, for example in offices and homes. These systems remove pre-existing particles (for example smoke), but do not remove toxic gases and other polluting compounds which are not in the form of particles.
Ozone is currently used to remove smells in many fields. Examples are kitchen exhaust, livestock barns and wastewater treatment plants. However the products of ozonolysis are typically more irritating and toxic than the original compounds so this is not a satisfactory solution as the air must be diluted substantially before it is safe to breathe.
UV light is used in air circulation systems of some hospitals to sterilize air. However, this application is not able to remove many types of pollution including most gas phase chemicals and particles.
The object of the present invention is to meet the demand of a universal or “broad-spectrum” removal of air pollution in an efficient and simple way with minimum energy consumption.